#include <iostream>
#include <algorithm>
using namespace std;

int main(){
	int diff,n;
	cin >> n;
	int x[n];
	for(int i = 0;i < n;i++) cin >> x[i];
	sort(x,x + n);
	diff = x[1] - x[0];
	bool f = true;
	for(int i = 2;i < n;i++) if(x[i] - x[i - 1] != diff || x[i] - x[i - 1] == 0 || diff == 0) f = false;
	cout << (f ? "YES" : "NO") << endl;
}